Abrasive blast table



Nov. 16, 1948. c. M. GOS-SAR'D 2,454,158

ABRASIVE BLAST TABLE Filed Oct. 5, 1945 I 6 Shets-Sheet 2 6 Sheets-Sheet 4 Filed Oct. 5, 1945 l5 mam .55 M m QM Nav. 16, 1948.

Filed Oct. 3, 1945 7 C M. GOSSARD ABRASIVE BLAST TABLE 6 Sheets-Sheet 5 Ul/QFLESM.

NOV. 16, c M GQSSA'RD ABRAS IVE BLAST TABLE Filed Oct. 3, 1945 6 Sheets Sheet 6 o o o grwwwtom M43455 mnaosa/wao,

Patented Nov. 16, 1948 ABRASIVE BLAST TABLE Charles M. Gossard, Hagerstown, Md., assignor toPangborn Corporation, Hagerstown, Md.', a corporation of Maryland Application October 3, 1945, Serial No. 619,994

7 Claims. (C1. 519) The present invention relates to abrasive blast ing apparatus of the character wherein articles are coveyed through a blast zone, and more specifically pertains to a rotatable table-like structure carrying a plurality of rotary auxiliary tables which support and turn the articles as they pass through the blast zone. The invention is characterized. by position and orientation of the abrasive blast stream in relation to the movement of the auxiliary tables so as to provide a more uniform distribution of the projected abrasive over the surface of the auxiliary tables and the articles supported thereon.

An object of the invention is to provide abrasive blasting apparatus wherein the over-blasting of certain areas of the small auxiliary table surfaces and under-blasting of other portions of the table surfaces and the articles supported thereon is avoided, and to provide apparatus wherein the impingement pattern is more uniformly distributed over the surface of the small rotatable auxiliary tables and the articles thereon. V

A further object of the invention is'to direct the abrasive blast stream of an elongated pattern in such a direction and orientation as to more uniformly distribute the abrasive over the articles supported on auxiliary tables as these auxiliary tables rotate while moving through the blast stream.

Other objects and features of the invention will be more apparent as the present disclosure proceeds and upon consideration of the accompanying drawings and following detailed description wherein an illustrative type of apparatus em bodying the invention is disclosed.

In. the drawings:

Fig. 1 is a front elevational View of an abrasive blasting table assembly embodying the invention.

Fig. 2 is a side elevational view of the apparatus shown in Fig. 1. I

Fig. 3 is a plan View.

Fig. 4 is a sectional view of the main table illustrating the mounting of one of the auxiliary tables.

Fig. 5 is a sectional plan View taken. approximately on the line 5-5 of Fig. 4 illustrating the drive for the auxiliary tables and the abrasive scrapers. l 1

Fig. 6 is a fragmentary sectional plan view taken substantially on the line 6-5 of Fig. 4.

Fig. 7 is a diagram illustrating increments of movement of one of the small tables in passing through one blast zone. y

Fig. 8 is a diagrammatic View illustrating the and moved through the blast zone.

2. manner in which a generally fan shaped abrasive blast stream is produced.

Fig. 9 is a diagrammatic View illustrating the relationship of an auxiliary table to the elongated pattern of the blast stream when this auxiliary table is in the position 9 of Fig. 7.

Fig. 10 diagrammatically illustrates the relationship of the elongated pattern of the blast stream with respect to the auxiliary table as it moves into the position ID of Fig. '7.

Fig. 11 diagrammatically shows the relationship of the elongated blast stream to the auxiliary table in proceeding into the position ll of Fig. 7.

Fig. 12 illustrates the manner in which the elongated pattern of the blast stream impinges on the auxiliary table in moving into the position l2 of Fig. '7.

Fig. 13 diagrammatically shows the relationship of the elongated blast pattern to the auxiliary table in proceeding into the position 13 of Fig. '7.

Fig. 14 diagrammatically shows the relationship of the elongated pattern of the blast stream with respect to the auxiliary table as this table moves into the position I4 of Fig. 7.

Fig. 15 diagrammatically shows the relationship of the blast stream as the auxiliary table moves into the position 15 of Fig. 7.

The present invention relates to a table-like structure carrying a plurality of auxiliary tables on which articles to be subjected to the impingement of an abrasive blast stream are supported The main table supports and moves the auxiliary tables in an orbital path around the axis of the main table. The small or auxiliary tables are rotated during the translatory movement, and particularly while passing into and through the blast zone.

The prior art includes work handling mechanisms of this typewherein abrasive is projected into impingement with articles supported on auxiliary tables. Apparatus of this type is disclosed in the patent to Rosenberger 2,315,546 wherein the abrasive is projected by a throwing wheel to provide a downwardly directed generally fanshaped stream of abrasive particles. In the prior art such as represented by this Rosenberger patent, the elongated pattern of thefan-shaped blast stream is arranged substantially parallel to the orbital movement of the auxiliary tables, or in a plane substantially at right angles to the radiusof the main table. Such an arrangement provides an uneven or non-uniform distribution of the projected abrasive over the surface of the auxiliary table, and accordingly overblasting of certain surface areas of the articles supported on the auxiliary table, and underblasting of other surface areas of the articles. In such prior apparatus the major axis of the elongated blast stream is always arranged along a radius of each auxiliary table, and for a portion of the blasting period the elongated pattern extends through the. center, of the auxiliary-i table: and also impinges thereonwas a diameterof' therotating auxiliary table. Accordingly there is overblasting of that portion of the articles adjacent the axis of the small table, and underblasting of the surface area of the articles adjacent the periphery of the auxiliaryutable.

The present invention pertainstot apparatus wherein overblasting of portions of the articles supported on the auxiliary tablessisavoided. and underblasting of other surface areas of the articles is likewise avoided to provide a more uniform distribution of the impingement of the abrasive on H the-v articles. 3 These iobjects and, advantagesare realized by the apparatusrillustrated in the --drawi ngs whereinthe elongated pattern of the abrasive .blast; stream is arranged substantially at right angles .to .theupath of -.mo yement of the auxiliary erably is so rotated as to drive the main table in a clockwise direction, as indicated by the arrow 30 in Fig. 3. The motor 28 is also of the variable speed type so that the speed at which the main table is rotated may be altered. The apparatus includes means (not shown) for maintaining the pulley 33 in firm frictional engagement with the a track 3,4.- iThewpulley 33:.andassociatedparts are encased in-a suitable housingfafi. Thus the auxiliary tables 24 are bodily moved through the housing from the loading station and returned to the original position where the articles may be removed from the small tables.

The auxiliary tables 24 are circumferentially spaced-around the main table and may be of any suitablesizedepending upon the type of articles to be treated and the dimensions of the main table in relation to the diameter of the small tables. .FIH' the exemplary embodiment illustrated in the tables or substantially on a. radius of the main table.

Referring to. thedrawings, there is shown. in Figs. 3 and. 4 amaintable-likestructure represented generally at 2B which is mounted for rota- .tion.=in:a substantially horizontal plane in any suitable manner, such-.asqby means ofa vertical shaftZl (Fig. 5) depending. from. the main .table, .and rotatable ,in; suitable bearing assembly indirated. at 19. The main table. is substantially :en,

.ca sed. -w,ithi-na.;housing 231Which is. cut away along the forward portion to provide a load and unload- .ing stationwhere-a portion of the maintable .is: exposed, and. where-the articles, to .be. blast itreated may. .be. loaded onto auxiliary. .tables 24 and removed thereform after being subjectedito the .blast ztreatment; The opening in the housing adjacent, the-- loading-zstation is provided with, a curtain-pfthe. conventional type comprisinga plurality of rubber orlike-strips 26dependingfrom:

. path around the axis ofthe main table. The .driv-..

,ing mechanism forrthe mainv table structure,in- -.cludes a motor Zllmounted at .the top portion of thehousing. Themotor. 28 drives ayertically depending shaft 3 I through a speed reducing; mechanism: 3201 any conventional type. Theshaft. 3 l carries apulley 33 atthelower endthereofwhich ;irictionally-engagesan annulartrack 34 arranged around theperiphery of the. maintable structure.

The track-34, is rigidly secured to themain table structure and:thedepending-portion of.;.the tra;ck is reniforced by a. plurality: of .rods 35..W hich are adjustableinlength. The inner ,endsof these rods are :seated in. sockets. 3.1 .carriedby. bearing .assemblies 4t=for the auxiliary tables. The motor ,28. maybeoperated. in either. direction, but pref least a portion ofv the housing.

vzone and during. translatory. movement of the adapted to engage an annular, member. 43 during a portion of one revolution of thevmain vtable. The annular member. 43 describesa substantially perfect circle but. isv eccentricallyarranged with. respect totheaxis of. themain table, and with respect to theaxisof the..shaft.2l. The .center. of

v.the annularmember Ali-is. accordingly displaced fromthe axis of the shaftil, as indicated at. D in Fig, 5...This displacementof the axis of the maintablefrom the center. of the annular mem- ..ber-.43,is. so. chosen .that the periphery of each of. thev Wheels 427will engage the annular member 43 at approximately'the nine oclock positionin Figs. 3 and5, and remain. in engagement withthe annulanmember 43, until they auxiliary tables arrive approximately in the three oclock position. The annular member43 is supported on a rotatable structure which supports the abrasive scrapers 47. Thisrotatable structure includes a hub portion 45' and a plurality of radially arranged arms or spokes as shown in Fig. 5. The annular member 43 is secured to the spokes 50 by means of a plurality of brackets 46. The hub portion 45 of this rotatable structure turns about an axis A which is displaced from the axis of the shaft 2| and a suitable bearing assembly forthis rotatable structure isshown at in Fig. 4.

The annular. member 43 is so constructed as to have resilient characteristics for driving the wheels; 42. In the embodiment illustrated, the annular member is iormedof a hollow tube, such --as-a.-rubber hose. The-wheels alsocarry-a friction surface such as a band of rubber orlike material; 44. The resilient.characteristics. of the annulardmember 43 permit theperipheral surfaces of. the .wheels 42. to engage the. tubular member-with .someldisplacement of the rubber tube so as to enhance the frictional engagement of each wheel Al-with theannularmember and ,5 thereby provide positive driving of the auxiliary tables 24. 1 i

The main table is provided with apertures through which the spent abrasive may pass downwardly for removal from the housing. The abrasive is conveyed into suitable hoppers for which it is returned to the abrasive projecting devices. The rotatable structure includes the abrasive scrapers 47 for moving the spent abrasive particles into the respective hoppers. abrasive scrapers have angular portions 48 and 49, which serve to shift the abrasive to a position for dropping into the hoppers arranged therebelow. The abrasive scrapers further reinforce the table structure and are mounted for rotation with the annular member 43 and for independent rotation with respect to the main table 20.

The mechanism for driving the abrasive scrapers includes a motor 5| mounted on a bracket 52 adjacent the upper part of the housing 23. The motor 5| drives a depending shaft 53 through a suitable speed reducing mechanism 54 mounted on the top portion of the housing 23, asshown in Figs. 3 and 4. The depending shaft 53 carries a friction wheel 56 at the lower end thereof rigidly keyed to or otherwise secured to the shaft 53. The wheel 56 carries a frictional surface and is adapted to engage an annular track member 51, as shown in Figs. 4 and 5. The annular track 51 is rigidly secured to the spokes 56 of the rotatable structure supporting the abrasive scrapers 41. Thus when the shaft 53 is driven, the abrasive scrapers 41 are rotated by reason of the driving engagement of the pulley 56 with the track 51. The wheel 56 is maintained in firm frictional engagement with the track 51 by a suitable resilient device, shown generally at 58. The shaft 53 and pulley 56 and associated parts are encased within a supplemental housing 59. The motor 5| may be of the variable speed type, and the transmission mechanism as represented by the speed reducer 54 is also of the type whereby the speed of shaft 53 may be varied so as to vary the speed at which the abrasive scrapers 41 are moved. Thus the abrasive scrapers may be driven at such a speed so as to insure that all of the spent abrasive is conveyed to a position for dropping into the respective hoppers regardless of the volume of abrasive projected by the abrasive propelling device and independently of the drive for the main table 20.

In apparatus exhibiting the invention, the abrasive is projected as a forceful stream downwardly into the path of movement described by the auxiliary tables 24. A characteristic feature of the invention is that a forceful abrasive stream of elongated pattern resembling a generally fanshaped blast stream is employed for impingement upon the articles carried by the auxiliary tables and so oriented that the elongated pattern is in a position generally at right angles to the orbital movement of the small tables 24.

elongated blast pattern is that of an abrasive throwing wheel, diagrammatically represented in Fig. 8, wherein the abrasive is projected in a generally fan-shaped stream, as indicated by the H the elliptical area 61 represents substantially'the The position and extent of the blast stream with respect'to the auxiliary tables 24. Such a blast stream may be provided by an abrasive throwing wheel 6| such as disclosed in the patent to Keefer 2,320,364. The abrasive throwing wheel is mounted within a protective housing 62, and the wheel is driven by means of a motor 63. Thus when abrasive is fed to the transfer mechanism of the wheel through a feed spout 54, and when the wheel is rotated, a generally fan-shaped blast stream will be projected downwardly in the housing 23. The length of the elongated pattern is greater than the diameter of the auxiliary tables 24. The wheel 6| may be rotated in either direction, but is preferably driven in the direction of the arrow 66, shown in Fig. 3.

The apparatus may include an additional abrasive projecting device so as to provide two abrasive blast streams through which the articles carried by the small auxiliary tables 24 pass during one revolution of the main table20. The second abrasive projecting device is represented generally at 1| and includes an abrasive throwing One type of abrasive projecting device providing an" hoppers 88 and 89.

wheel which may also be of the type disclosed in the Keefer Patent 2,320,364. This wheel may be rotated in the direction of the arrow 12. A motor 13 drives the wheel which is arranged within a protective housing 14. Thus when abrasive is supplied to thefeed spout 16 and the wheel is driven, a downwardly directed forceful abrasive stream will be established, and the abrasive particles will be projected so as to have a pattern somewhat like that shown by the elliptical area 11 at the point of impingement with the articles on the small tables '24. Itwill be observed that the elongated pattern of this abrasive stream is also arranged with the major dimension at substantially right angles to the path of movement of the auxiliary tables 24. Likewise the blast pattern 11 is slightly greater in length than th diameter of the auxiliary tables.

The apparatus illustrated includes the feature of projecting the abrasive downwardly at an angle to a vertical plane so that the abrasive stream 61 is arranged at an acute angle with respect to the horizontal surfaces of the auxiliary tables 24, and therefore provides for impingement of the abrasive on the more vertical surfaces of the articles supported on the auxiliary tables. This angular projection of the abrasive particles is provided by mounting the wheel 6| at an angle, as shown in Figs. 1 and 3. A similar angular mounting of the wheel 1| provides that the abrasive projected thereby moves downwardly and at an acute angle with respect to the horizontal surfaces of the auxiliary tables 24.

The spent abrasive delivered into the hoppers by means of the abrasive scrapers 41 is returned to a position for being supplied to the abrasive projecting devices by means of elevators shown at 18 and 19. These elevating type conveyors are of well known construction and include buckets or cups (not shown) carried by an endless belt. The endless belts are driven in a well known manner by means of motors 8| and 82 along with suitable transmission mechanisms 83 and 84. The abrasive lifted by the elevators then moves respectively into separators 86 and 81 from which the clean abrasive moves into The feed spout 64 guides abrasive from the hopper 89 to the abrasive projecting device 6| and the feed spout 16 guides abrasive from the hopper 88 to the abrasive projecting device 1|. A valve 9| is associated 1 forceful streams.

7 with the hopp'er 88 for interrupting the: flow of abrasive to the feed spout 16. This valve may be actuated by a handle 92 which: extends. to apositionadjacent the loading and unloading station at the front of. the housing 23. A similar valve 93 is associated with the. hopper 89 for controllin the flow of. abrasive to the feed spout 64. This valve 93 may be actuated by a handle. 94 which extends to a position adjacent the loading and; unloading station.

The articles to be treated by the forceful stream of abrasive particles are arranged on an auxiliary table 2 4 which is then exposed outside the housing 23 and positioned in theloading station; .The motor 23 is energized to drive the friction wheel 33 andthereby rotate the main table 26 in the direction of the arrow 36-. The speed at which the main table is driven may be varied by adjusting the speed of the motor or by adjusting the position of the hand wheel 96 so as to alter the ratio of the speed reducing mechanism 3 2. The auxiliary table while in the loading station does not rotate about the axis of the associated shaft ll, since the wheel G2 is not then in engagement with the annular member 43,' as will be apparent from a consideration of Fig. 5.

Themotors 63- and i3 are also energized to drive the abrasive throwing wheels preferably in the directions indicated by the arrows 66 and 1 2. The valves 9| and 93 are opened to admit abrasive to the feedspouts 16 and 64 whereby the twowheels project abrasive in fan-shaped The motor is also energized to drive the friction wheel 56 and thereby rotate the abrasive scrapers 4? and the rotatable structure "carrying the annular member 43. The abrasive scrapers and the associated structure is preferably driven in a counterclockwise direction as viewed in Fig, 5 and indicated by the arrow 91.

As the auxiliary table 2 K moves'into the housing 23 and arrives at approximately the nine oclock position, the associated wheel 42 engages the annular member 43 and the auxiliary table thus begins to rotate in a counterclockwise direction about the axis of the shaft 4| as viewed in Figs. 3 and 5. In the meantime other auxiliary tables 24 arrive at the loading and unloading station where articles which have been previously subjected to the impingement of the abrasive particles are removed and other articles arranged on these tables for movement through the housing.

as one of the auxiliary tables moves into this' blast zone and into the position 9 of Fig. 7, the elongated blast stream will traverse the peripheral portion of the auxiliary table in a chordlike manner, as shown in Fig, 9. This auxiliary table is then rotating in the direction of the" arrow 98 and bodily moving with the main table 20. Accordingly the peripheral portion of the auxiliary table and the articles supported thereon are subjected to the impingement of the abrasive stream with the major dimension of the blast pattern defining an infinite number of chords with respect to the auxiliary table 24.

The auxiliary table, while moved bodily with the main table 20, moves into the increment position-shown at It in Fig. 7 and the major dimen-' 8 sion of the elongated. blast pattern continues to impinge upon the auxiliary table in a manner: as

diagrammatically illustrated in Fig. 10 wherein all of the previous relative positions of the blast stream have been. omitted for the purpose. of clearly depicting the manner in which the elongated pattern of the blast stream scans or impinges upon the surface of the auxiliary table and the articles supported thereon. It will be observed that the'major dimension of the blast stream continues to be arranged in a chord-like manner with reference to the auxiliary table and the elongated pattern defines an infinite number of chords intermediate those illustrated in Figs. 9 and 10.

The auxiliary table 24, continues moving bodily through the blast stream 11 and. also continues rotating in the direction of the arrow 98 ,and therefore arrives in the position diagrammatically shown at H: in Fig. 7- where the elongated pattern of the blast stream is defining chords with respect to theauxiliary tableand positioned near thecenter of the auxiliary table, as shown. in Fig. 11. The auxiliary table in moving to the next increment position, as shown in Fig. 12, continues to rotate in the direction of the arrow 98, and the major dimension of the blast stream then approaches the center of the auxiliary table so that the chordal arrangement of the elongated pattern represents a diameter of the auxiliary table.

As the auxiliary table 24 continues to move bodily through this blast stream, the elongated pattern retracts from the diameter arrangement and re-scansthe surface of the auxiliary table, as shown progressively in Figs. 13 to 15, where the peripheral portion is again subjected to an impingement of the abrasive wherein the major dimension of the blast stream is arranged in a chord-like position relative to the auxiliary table and eventually the auxiliary table and the articles supported thereon pass beyond the blast zone as represented by the area 11. A further feature of the apparatus includes the second. blast .zone represented by the area 61. The auxiliary tables 24 in moving through this blast zone are subjected to an impingement pattern like that-shown and described in connection with Figs. 9 and 15.

As the auxiliary tables are bodily moved through the housing 23 and arrive at substantially the three oclock position as viewed in Fig.

3, the associated friction wheel 42 moves from engagement with the annular member 43 and accordingly the auxiliary table is no'longer positively driven. The auxiliary table therefore ceases rotating about the axis of the shaft 4| and is bodily moved in thisstate to the unloading station.

It will be observed that the auxiliary tables 24 are driven as they are bodily moved into one of the blast zones so that these auxiliary tables rotate while passing through the blast streams.

-The major dimension of the elongated blast stream therefore impinges upon the article supported on an auxiliary table in a chord-like relationship so that the elongated pattern of the abrasive particles engage the article in an infinite number of chords so as to more uniformly distribute the abrasive over the surface of the articles. This novel result is in contrast to the prior art wherein the elongated pattern of the blast stream. is arranged on substantially av radius of the main table which provides for over-blasting of surfaces of the articles adjacentthe axis of the auxiliary table, and under-blasting of those 9 surface areas of the articles adjacent the periphery of the auxiliary table.

While the invention has been described with reference to specific structural features of a table-like structure carrying auxiliary tables including a specific driving arrangement for the main table and the auxiliary tables, it is apparent that changes may be made in these features. Such modifications may be made without departing from the spirit or the scope of the invention as set forth in the appended claims.

I claim:

1. Apparatus for blast treating articles comprising, a main table supported for rotation in a substantially horizontal plane, an auxiliary table supported on said main table and rotatable about a substantially vertical axis, means for rotating said main table to move said auxiliary table in an orbital path, means for projecting abrasive at a blasting velocity downwardly in a substantially fan-shaped stream, said projecting means being so arranged that the elongated pattern of the abrasive blast stream is substantially at right angles to the orbital movement of said auxiliary table, and means for rotating the auxiliary table while moving through the blast stream.

2. Apparatus for blast treating articles comprising a support mounted for rotation in a substantially horizontal plane, a Work table carried by said support and rotatable about a substantially vertical axis, means for rotating said support and table to impart orbital motion to said table, means for projecting treating particles at a blasting velocity downwardly in a substantially fan-shaped stream, said projecting means being so arranged that the elongated impingement pattern of the fan-shaped blast stream scans said moving table in paths constituting a family of chords varying progressively from chords tangent to an edge of the table to chords extending diametrically across said table.

3. Apparatus for blast treating articles comprising a support mounted for rotation in a sub stantially horizontal plane, a work table carried by said support and rotatable about a substantially vertical axis, means for rotating said support and table to impart orbital motion to said table, means for projecting treating particles at a blasting velocity downwardly in a substantially fan-shaped stream, said projecting means being so arranged that the plane of the blast stream intersects the orbital plane of the table at an acute angle and scans said moving table obliquely in paths constituting a family of chords varying progressively from chords tangent to an edge of the table to chords extending diametrically across said table.

4. Apparatus for blast treating articles comprising a support mounted for rotation in a substantially horizontal plane, a Work table carried by said support and rotatable about a substantially vertical axis, means for rotating said support and table to impart orbital motion to said table, means for projecting treating particles at a blasting velocity downwardly in a substantially fan-shaped stream, said projecting means being so arranged that the elongated impingement pattern of the fan-shaped blast stream strikes the orbital plane of the table along a trace substantially at right angles to the orbit of movement of the table so that it scans said moving table in paths constituting a family of chords varying progressively from chords tangent to an edge of 10 the table to chords extending diametrically across said table.

5. Apparatus for blast treating articles comprising a support mounted for rotation in a substantially horizontal plane, a work table carried by said Support and rotatable about a substantially vertical axis, means for rotating said support and table to impart orbital motion to said table, means for projecting treating particles at a blasting velocity downwardly in a substantially fan-shaped stream, said projecting means being so arranged that the plane of the fan-shaped blast stream intersects the orbital path of the table at an acute angle and along a trace substantially at right angles to the orbit of movement of said table so that it scans said moving table obliquely in paths constituting a family of chords varying progressively from chords tangent to an edge of the table to chords extending diametrically across said table.

6. Apparatus for blast treating articles comprising a support mounted for rotation in a substantially horizontal plane, a work table carried by said support and rotatable about a substantially vertical axis, means for rotating said support and table to impart orbital motion to said table, means for projecting treating particles at a blasting velocity in a substantially fan-shaped stream, said projecting means being located outside the vertical projection of the orbital path of movement of said table and being arranged to throw its blast stream inwardly and downwardly across said orbital path so that the plane of the fan-shaped blast stream intersects the orbital plane of the table along a trace extending crosswise of the orbit of movement of the table, whereby the blast stream scans said moving table in paths constituting a family of chords varying progressively from chords tangent to an edge of the table to chords extending diametrically across said table.

7. Apparatus for blast treating articles comprising a support mounted for rotation in a substantially horizontal plane, a work table carried by said support and rotatable about a substantially vertical axis, means for rotating said support and table to impart orbital motion to said table, means for projecting treating particles at a blasting velocity in a substantially fan-shaped stream, said projecting means being located outside the vertical projection of the orbital path of movement of said table, and being arranged to throw its blast stream inwardly and downwardly across said orbital path with the plane of the fan-shaped blast stream intersecting the orbital path of the table at an acute angle and along a trace extending crosswise of the orbit of movement of the table so that the blast stream scans said moving table obliquely in paths constituting a family of chords varying progressively from chords tangent to an edge of the table to chords extending diametrically across said table.

CHARLES M. GOSSARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 919,417 Carroll Apr. 27, 1909 2,276,345 Rosenberger Mar. 17, 1942 2,315,546 Rosenberger Apr. 6, 1943 

